Slack adjusters are well known components which are provided in the brake rigging of railway vehicles to automatically adjust the slack in such brake rigging for a number of reasons. One such reason is that the slack adjuster automatically maintains the brake cylinder piston rod travel within a preselected travel distance. Maintaining such brake cylinder piston rod travel distance within the prescribed limit is of particular importance in present day higher speed train operations. Another important reason is that the slack adjusters will provide a substantially more uniform braking force to be applied to each set of wheels on each car making up a train. Because of the improvement in providing a more uniform braking force, the undesirable possibility of some cars in the train being held back while other cars roll ahead is generally minimized. A third reason is that in a truck-mounted braking system, a slack adjuster may be used to replace one of the brake cylinders of the brake rigging resulting in considerable cost reduction and weight savings.
A double-acting compression actuatable slack adjuster to adjust the slack in a railway vehicle brake rigging, as shown in FIG. 1, typically includes an elongated hollow housing member connectable at a first end thereof to a brake rigging, an elongated rod member which is also connectable at a first end thereof to such brake rigging and has a threaded portion at least adjacent a second end thereof. This threaded portion of the rod member extends into and is reciprocally movable within the housing through a second end of the housing. A movable positioning means is threadedly engaged with the threaded portion of the rod member intermediate the ends thereof. This positioning means rotates about the threaded portion of the rod member when in the disengaged position thereby changing the length of the slack adjuster assembly by changing the relative longitudinal position between the housing and the rod member. A pair of abutment surfaces, a pair of urging means, and an overtravel control system are provided for controlling the movement of this positioning means in response to the travel distance of a brake cylinder piston connected to the brake rigging.
When properly installed in the brake rigging, the slack adjuster will maintain specified piston travel at all times. The unit will automatically lengthen on one of the release and application of a brake to adjust for brake shoe wear. When worn shoes are replaced, the unit can be shortened to provide proper piston travel on the forward stroke of the first brake application.
A slack adjuster must be carefully packaged to avoid accidental let out of the slack adjuster and turning of the jaw member during shipping and handling. Either of these occurrences could lead to difficulty during installation of the slack adjuster in the brake rigging.